1. Field of the Invention
The field of the present invention relates to a probe for monitoring a pressurised process, and to a method for monitoring a process in which one or more hazardous substances occur.
2. Background
Chemical production processes can be controlled efficiently when the instantaneous composition and quality of starting substances, reaction mixtures or products in the various stages of the production process are known. Online spectroscopic measurement methods allow direct continuous monitoring of a running process. Optical probes are of particular importance here, since analysis by means of optical probes takes place noninvasively in direct sample contact and works without elaborate sampling or preparation of the substance mixture to be analysed.
For usability of optical probes, access to the substance or substance mixture to be examined is crucial. Chemical processes are conventionally carried out in closed reactor containers and/or pipelines. These are generally opaque for the wavelength range which is used for the analysis.
It is therefore necessary to provide windows which are transparent for the wavelength range being used, in order to make it possible to track the processes in the reactor space or the connected pipelines.
Owing to possible toxic properties of the substances to be analysed in the process, stringent requirements are placed on these windows in respect of leaktightness, particularly for processes which are operated under high pressure.
For the input and output of electromagnetic radiation in a reactor, so-called coupling lines are often used. These are flexible lines which make it possible to transmit electromagnetic radiation over a certain path without accurate positioning of the optical components along this path being necessary. Above all, glass fibre cables from the telecommunications field are known. In process monitoring or online analysis, so-called waveguide couplings or special silver halide or fluoride glass light guides are used for applications in the medium infrared range. In the near infrared range and ultraviolet/visible range (UV/Vis: 200-700 nm), it is preferable to use quartz light guides which are available with low attenuation in this spectral range.
The publication DE10230857A1 describes a process window for online analysis with pressure monitoring. At two opposite positions of a pipe, two windows are formed through which electromagnetic radiation can be input into the pipe and output again. Each window is placed into a threaded insert. Respectively, 2 seals between the threaded insert and the pipe, and between the window and the threaded insert, ensure sealing of the pipe interior from the outside world. The threaded insert is screwed into a holder (measurement cell body), which is connected to the pipe. Both between the threaded insert and the window, and between the threaded insert and the holder, there are cavities between the first and second seals, and these are connected to one another via bores. The cavities are sealed off from the outside world by means of a seal between the threaded insert and the holder. There is double sealing of the pipe interior from the outside world by means of the process window. Besides this double security, the device makes it possible to monitor leaks. If one of the seals, which is in contact with the pipe interior, loses its effect, substances emerge from the pressurised pipe into the cavities. The rising pressure can be registered by means of a pressure sensor, which is connected to the cavities.
The dimensions and geometries of optical probes, and the optical components contained in them, do not allow double sealing respectively at a window in the form of the process window disclosed in DE10230857A1. It is furthermore generally known that light guides and waveguides are mechanically loadable much less strongly than, for example, a quartz glass or sapphire window, as are used in a process window according to DE10230857A1.
Accordingly, pressure-tight sealing of a light guide or waveguide is also more demanding and/or more elaborate.
In the probes commercially available nowadays, the light guide or waveguide per se is therefore not sealed off from the process space, but instead the light is input from a source via a first coupling line through a window into the process space and output again through another window or the same window, in order to reach a detector via a second coupling line, the sealing of the process space from the outside world (in which the coupling lines are located) being carried out by means of a seal between the window and the process space.
This is disclosed, for example, in patent specification DE4414975C2. In FIG. 2 of the said patent specification, a pressure-proof window is sealed off from a casing by a seal. In the casing, light guides are arranged which input and output the light through the window into the reaction space. As a particular feature in the device in FIG. 2, the light guides are additionally connected to the casing by means of an adhesive. These adhesive bonds are intended to form pressure-proof barriers. Such an additional pressure barrier, however, is not generally usable since many substances, for example solvents or strong oxidising agents, dissolve the adhesive or react with the adhesive so that this barrier is destroyed. An adhesive bond is furthermore not a defined connection which ensures process-compatible sealing in respect of pressure-tightness, thermal stability and chemical stability.
Other probes described in the prior art comprise a simple seal, by which the process space is sealed off by means of a window from the probe optics (see for example U.S. Pat. Nos. 5,185,834, 5,170,056, 4,835,389, 4,988,195, 5,051,551, DE-A4038354). In processes which take place under pressure, there is a risk of a window breaking or a leak at a seal, so that substances from the process can reach the outside world. Besides the risk of damaging the probe optics, in the case of toxic substances in particular there is also a risk of harming humans and the environment.
On this basis, a probe is desired which allows online monitoring of a pressurised process and has safety precautions which effectively prevent substances from emerging from the process space into the environment if a seal placed in contact with the process space fails.